Field of the Invention
The present invention relates to a method and apparatus to perform the contents analysis of C, H, N and S. in samples, by their flash combustion in oxygen.
Apparatuses are known of the type mentioned and are called elemental analysers, basically consisting of a so-called combustion chamber kept at high temperature (around 900xc2x0 C.) in which the sample to be analysed is introduced.
The chamber, normally flushed out by a flow of inert gas, is fed with oxygen to carry out said flash combustion, whose products are then sent to a reduction reactor and the chemical analysis apparatus.
It is very important, for analysis cost reasons and the maintenance of efficiency of the reduced copper which is present the reduction reactor, to provide an oxygen supply calibrated on the quantity actually necessary to carry out the sample combustion.
The collection of a certain amount of oxygen in a duct (loop) has already been suggested, to be sent to the combustion chamber after passing through the inert gas. Nevertheless, this preset amount must be chosen so as to guarantee the combustion of each sample type and weight hence, for samples requiring less oxygen or those of lesser weight, a part of the oxygen supplied is not involved in combustion and enters into the system downstream, oxidising the reducing layer and therefore causing an undue excessive copper consumption, as well as an undue excessive oxygen consumption.
To avoid this happening, the proposal has been made (Italian Patent Application No. M198A 000435 of 4/3/98) to supply oxygen directly through a valve system and to determine a priori the amount, taking into account the nature and weight of the sample to be analysed. This allows the exact measurement of the oxygen needed, but requires prior knowledge of the sample nature and also involves the presence of control software of lengthy and complex preparation.
It would be desirable to control the quantity of oxygen supplied each time, so as to correlate it to combustion needs (sample nature and quantity), setting aside knowledge of the sample characteristics and intervening to halt the oxygen supply each time when combustion is completed.
For the implementation of such a method, the parameter used to exercise influence over the time progression may consist of the brightness induced by the combustion in the combustion reactor, the temperature in the same combustion reactor or finally, the pressure in the combustion reactor, or upstream thereof, in the gas supply circuit.